So-called parallel kinematic structures are known. For example, U.S. Pat. No. 6,453,566 B1, U.S. Pat. No. 6,467,762 B1, U.S. Pat. No. 6,871,584 B2, EP 218546 B1 and EP 250 470 B1 disclose structures of this type.
Non-parallel kinematic structures providing up to 6 degrees of freedom (DOFs) usually offer large motion ranges but have a high inertia because actuators are arranged within and carried by the structure and have a low stiffness because forces and torques are transmitted through a single kinematic chain. As a result, mechanical eigen-frequencies are commonly low.
Parallel kinematic structures also providing up to 6 DOFs allow to reduce inertia because heavy components (e.g. actuators) may be arranged on ground and to increase stiffness because more than one kinematic chain acts “in parallel” on an end-effector. However, their motion ranges may be, as compared with non-parallel kinematic structures, reduced.